Musings on Science

Daily Roundup: From Ophthalmology to Oncology

Remember those vaguely annoying, slightly terrifying camera-looking things ophthalmologists use to check your eyes? For me, those were always a source of mingled fascination and terror; I kept imagining invisible beams of… something… piercing my eyes as I sat with chin wedged firmly into the machine.

Invisible beams of something they were — but it was simply light. Near-infrared light, to be precise, and doctors have been using this method, called optical coherence tomography (OCT), to see through the layers of the retina for a couple of decades. And now, researchers in Europe have come up with a way of scanning just beneath the surface of the skin to identify potential lesions and cancerous regions.

As the press release states, abnormal tissue in humans manifests itself in the blood vessel network as unusually large blood vessels, very close to the skin surface. The researchers surmise that the higher blood supply would be necessary for tumorous regions, which divide uncontrollably and need energy to sustain that level of cellular division.

The technique of OCT itself is pretty fascinating and there’s a high-level (at least, until the third paragraph) explanation at this site. It’s essentially ultrasound — but with light instead of sound waves. There’s a problem, however; light travels about 200,000 times faster than sound in tissue. If you were measuring how long it takes for the echo of the light to arrive back from the tissue, you would need electronic equipment with time resolution much more advanced than what’s currently available.

Enter the Michelson apparatus.

I must take yet another detour here and state that I think the Michelson-Morley experiment, which provides the scientific equipment for this group of researchers’ endeavors, is one of the most elegant experiments of all time.

At the time Michelson designed his experiment, the scientific world was engulfed with the question of the aether. If light wasn’t a particle (but was), and wasn’t a wave (but was), what was it? “What was doing the waving?” asks George Johnson, in his lovely book The Ten Most Beautiful Experiments.

It was theorized that an invisible, massless wind must be doing this blowing, and the physicists terms it the ether or aether. But if it were truly there, then it must be having an effect on things. For instance, light. Michelson reasoned that if he measured the “echo” from light traveling first with the aether, then crosswise against the aether, then he should see the difference in time between the echoes and therefore the speed of the aether itself.

Angling two sets of mirrors perpendicular and parallel to the theorized ether, Michelson was eventually able to determine that if there were an aether it was incredibly well hidden. In fact, there was no aether.

The OCT method is a rather nice vindication of this expensive, time-consuming, and by some accounts marriage-wrecking experiment. The interferometer concept is now used in probing the depths of our eyes to find imperfections, and if our research friends in Europe are right, then it will be invaluable in the early detection of cancerous regions as well.